Phase-Exchange-Driven Wake-Up and Fatigue in Ferroelectric Hafnium Zirconium Oxide Films

Abstract

Ferroelectric hafnium zirconium oxide holds great promise for a broad spectrum of complementary metal–oxide–semiconductor (CMOS) compatible and scaled microelectronic applications, including memory, low-voltage transistors, and infrared sensors, among others. An outstanding challenge hindering the implementation of this material is polarization instability during field cycling. In this study, the nanoscale phenomena contributing to both polarization fatigue and wake-up are reported. Using synchrotron X-ray diffraction, the conversion of non-polar tetragonal and polar orthorhombic phases to a non-polar monoclinic phase while field cycling devices comprising noble metal contacts is observed. This phase exchange accompanies a diminishing ferroelectric remanent polarization and provides device-scale crystallographic evidence of phase exchange leading to ferroelectric fatigue in these structures. A reduction in the full width at half-maximum of the superimposed tetragonal (101) and orthorhombic (111) diffraction reflections is observed to accompany wake-up in structures comprising tantalum nitride and tungsten electrodes. Combined with polarization and relative permittivity measurements, the observed peak narrowing and a shift in position to lower angles is attributed, in part, to a phase exchange of the non-polar tetragonal to the polar orthorhombic phase during wake-up. These results provide insight into the role of electrodes in the performance of hafnium oxide-based ferroelectrics and mechanisms driving wake-up and fatigue, and demonstrate a non-destructive means to characterize the phase changes accompanying polarization instabilities.

Ferroelectric Properties and Polarization Fatigue of La:HfO2 Thin‐Film Capacitors

“…Although there are observations of large polarizations that are comparable with those of perovskite‐oxide ferroelectrics, doped HfO 2 thin films suffer from severe fatigue problems during bipolar electric field cycling. [ 21–30 ] Switchable polarizations ( P SW ) have been observed to be degraded to zero after ≈10 9 cycles in Hf 0.5 Zr 0.5 O 2 and Y:HfO 2 thin films. [ 22,28 ] In addition, dramatically increased leakage currents and dielectric breakdown appeared in fatigued HfO 2 thin films.…”

“…On one hand, the ferroelectric o‐phase is metastable and the transition to nonferroelectric phases may take place during electric field cycling, which results in the polarization degradations, as observed in Pt/Hf 0.5 Zr 0.5 O 2 /Pt thin‐film capacitors. [ 27 ] On the other hand, the pinning effect at non‐electroneutral ferroelectric domain walls by charged defects, which is also a main origin for polarization fatigue in conventional perovskite‐oxide ferroelectrics, [ 31,32 ] has been reported in Y:HfO 2 thin films. [ 28 ] Therefore, more effort is required to clarify the fatigue mechanism of HfO 2 thin films.…”

Wake‐Up Effect in HfO2‐Based Ferroelectric Films

“…The amount and distribution of oxygen vacancies are closely related to the electrode materials and the interfacial layers, so different trends of polarization response with field cycling depending on the electrode materials can be expected. [95] Investigations on the effects of TE in HfO 2 -based ferroelectric devices can be divided into different categories depending on the chosen material. The most common choice has been metal nitride electrodes, for example, TiN and TaN.…”

“…The amount and distribution of oxygen vacancies are closely related to the electrode materials and the interfacial layers, so different trends of polarization response with field cycling depending on the electrode materials can be expected. [ 95 ]…”

Wake‐Up Mechanisms in Ferroelectric Lanthanum‐Doped Hf0.5Zr0.5O2 Thin Films

“…In the literature, synchrotron‐based in situ XRD measurements during field‐cycling show measured phase changes typically in the sub 5% range even though P r increases more than 20–100% are reported. [ 18–21 ] Accordingly, phase changes during field‐cycling are present, but not the main mechanism to understand the wake‐up effect.…”